Jurors must decide who Whitey Bulger was

James "Whitey" Bulger, seen here in a booking mug shot from 2011, is on trial in federal court in Boston.

By Ron Allen and Tracy Connor, NBC News

A prosecutor and a defense lawyer presented jurors with dueling portraits of accused Boston mobster James "Whitey" Bulger on Wednesday: Was he a "hands-on killer" and top FBI informant or a small-time gangster who never squealed to the feds?

Nearly two decades after Bulger went on the lam, his federal racketeering trial is finally under way. The 83-year-old head of the Winter Hill Gang faces 32 counts, including 19 murders and accusations of money laundering, extortion, weapons and drugs.

In opening statements, Assistant U.S. Attorney Brian Kelly described Bulger as a cold-blooded kingpin who corrupted law-enforcement officials and controlled a crew of criminals who "ran amok" in Boston for nearly 30 years.

"It's a case about organized crime and public corruption," Kelly said.

"At the center of all the murder and mayhem is one man...James Bulger," he added.

The prosecutors described several murders and said Bulger didn't shy from violence.

"He did the dirty work himself," Kelly said, calling him a "hands-on killer."

The accusation that may have really stung Bulger, though, was about spilling secrets — not blood.

"Bulger was one of the biggest informants in Boston," Kelly said.

Even though the FBI has acknowledged that Bulger worked for the agency, he has denied it. And he hopes to convince jurors that he never broke the code of the streets.

"The evidence will show Bulger was never an informant," defense lawyer J.W. Carney said in his opening.

And the man who was one of America's most wanted for years, he said, was no criminal mastermind but a "small-time" bookmaker, loan shark and drug dealer who paid protection money to cops.

Carney made it clear he plans to attack the credibility of the prosecution's star witnesses: former Bulger cronies who made plea deals while their old pal was still on a run.

He zeroed in on John "The Executioner" Martorano, who spent 12 years in prison after admitting to 20 murders.

"The federal government was so desperate to have John Martorano testify ... they basically put their hands up in the air and said take anything you want," Carney said, the Associated Press reported.